Isocyanate is a main raw material for synthesis of polyurethane, and can be generally divided into an aliphatic category and an aromatic category. Although many types of the isocyanate are introduced in literatures, only the above two categories are actually applied. At present, there are two main types of polyurethane dressing, that is, one polyurethane dressing type taking aromatic isocyanates as raw materials, such, as toluene diisocynate (TDI) and diphenylmethane diisocyanate (MDI); and the other polyurethane dressing type taking aliphatic diisocyanates as raw materials, such as hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI) and isophorone diisocyanate (IPDI).
A U.S. Pat. No. 7,777,091 proposes a polyurethane system taking the toluene diisocynate (TDI) and the isophorone diisocyanate (IPDI) as main raw materials, wherein a polyether component is an ethylene oxide (EO)/propylene oxide (PO) tri-functional copolymer with high EO content. However, the material may produce toluenediamine (TDA), diphenylmethane toluene diamine (MDA) and other aromatic diamines in a degradation process when used in a medical dressing. Lots of toxicity experiments prove that the TDA and the MDA are strong cancerogenic substances capable of inducing gene mutation. Therefore, the polyurethane taking the aromatic isocyanates as the raw materials is not an ideal safety material.
A United States patent US 20110184080 (with an application number of U.S. Ser. No. 13/003,205) discloses a method of preparing a prepolymer from hexamethylene diisocyanate (HDI) and a polyether with high EO content, synthesizing hydrophilic isocyanate from a tri-functional HDI tripolymer and a mono-functional polyoxyethylene alcohol, and enabling a mixture of the prepolymer and the hydrophilic isocyanate to react under a combined action of water, a catalyst and a surfactant to produce a hydrophilic polyurethane foam material. The principal isocyanate is aliphatic diisocyanate such as the HDI. Hexamethylene-diamine (HDA) exists in a degradation product of such a polyurethane material. Although the substance is not carcinogenic aromatic diamine, the substance is still not a substance existing in a human body, and safety should be further verified. Meanwhile, a catalyst and other metal salts thereof should be added to serve as foaming assistants in a material preparation process, otherwise an ideal foam material cannot be obtained, and foam may suffer from expected intense contraction after foaming.